Fluorescent light dimming system



Jan 14, 1969 J. s. SPIRA ETAI. n 3,422,309

FLUORSCENT LIGHT DIMMING SYSTEM Filed Sept. 2l, 1966 Sheet Of 2 Jan,14,` 1969 A I J'. s.sP|RA ETAL 3,422,309

` FLUORESCENT LIGHT DIMMING SYSTEM4 Filed Sept. 2l, 1966 Sheet 2 of 2E'E M,

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wea/vf Y United States Patent O 5 Claims ABSTRACT F THE DISCLOSURE Alluorescent light dimmer for use in a two-wire system in which thedimmer has two leads connected in series with one wire of the two-wiresystem, while the ends of the two wires ofthe two-wire system areconnected across the primary winding of a ballast. The ballast primarywinding is connected in closed series relationship with a series ballastwinding anda fluorescent tube. Each of the ballast windings have smallwinding sections connected to the cathode heaters of thelluorescendtube.

This invention relates to a novel dimming circuit for fluorescentlights, and more specifically relates to a novel dimming circuit whereina controlled rectifier-type control means is connected between the inputsource of power and lthe primary winding of the fluorescent lightballast. This application is a continuation-in-part of copending'application Ser. No. 281,974, now abandoned, tiled May 21, 1963,entitled Fluorescent Light Dimming System, and assigned to the lassigneeof the present invention.

Dimmer circuits for dimming uorescent lights are well known to the art.Generally, such dimming circuits consist of some type of control meanssuch as adjustable resistors or autotransformers which vary the inputvoltage to the primary ofthe ballast. Such methods are subject to severelimitations of operation, since a small decrease in the voltage appliedto the ballast will not provide a voltage high enough to permit thelluorescent tube to strike an arc. Therefore, only a relatively smallrange of dimming is available before the iiuorescent tube drops out ofillumination. Generally, the best dimming ratio obtainable with thistype of variable input voltage to the ballast primary is of the order offrom Z-to-l to to1, and is impractical.

'Ilhe use of controlled tiring elements such as thyratrons or controlledrectifiers have also been used for dimming iluorescent lights. In allcases, however, the controlling devices are connected between theballast secondary winding and the lamp. While this gives satisfactoryoperation and a wide range of dimming, these arrangements require theuse of special dimming ballasts with elaborate auxiliary apparatus.

More important than this, however, the installation of such devicesrequires thaty three wires be connected from the dimming controlstructure as will be described more fully hereinafter. Therefore, When adimmer is to be applied to a presently existing two wire installation,new wiring must be run to the iluorescent lamp fixtures.

The principle of the present invention recognizes the desirability ofthe latter controlled rectifier-type control which was always usedbetween the ballast primary and tube, which gives Wide range control,and further recognizes the desirability of having a dimming controlstruc- 3,422,309 Patented Jan. 14, 1969 ture between the primary of theballast and the voltage source, which eliminates the need for runningadditional wires in a two-wire installation. More specifically, and inaccordance with the invention, the controlled rectiers of the firstmentioned species of units is used in the position of the lattermentioned species of units. Thus, in accordance with the invention, acontrolled rectiertype dimrning control is connected between the ballastprimary and the input voltage source.

When using this novel connection, applicant provides a system which hasthe advantage of simplified installation in presently existing two-wiresystems, yand moreover improves the dimming ratios made available bycontrolled rectifier-type operations wherein a high voltage pulse willbe transmitted to the tube even though the applied voltage is low inview of the intermittent type current conduction experienced with acontrolled rectifier-type device.

Accordingly, a primary object of this invention is to provide a noveldimming control structure for fluorescent lamps which gives smoothdimming down Ito a very low light intensity in a simple yand inexpensivemanner.

Another object of this invention is to provide a novel high ratio lightdimming 'structure for fluorescent lamps which can be easily installedin presently existing two-wire installations.

A still further object of this invention is to provide a controlledrectier-type device such as a controlled rectitier or thyratron orsimilar intermittently conductive device which is connected between theballast primary and input A-C line, and does not require a specialballast construction.

These and other objects of this invention Will becomel apparent fro-mthe following description when taken in connection with the drawings, inwhich:

FIGURE 1 illustrates a typical prior art dimming arrangement for afluorescent light which requires the connection of three wires.

FIGURE 2 illustrates a fluorescent light dimming circuit construction inaccordance with the invention wherein the dimmer structure has only twoterminals, and will pro vide a Wide dimming range.

FIGURE 3 illustrates the circuit of FIGURE 2 along with the provision ofa by-pass circuit for the dimming control circuit and an extending leadwhich could go to other primary circuits of other ballasts.

FIGURE 4 shows the wave form of the ballast primary voltage and ballastsecondary voltage in the circuit of FIGURE 3.

FIGURE 5 shows the wave form of tube current which flows intermittentlyunder the control of a gate controlled switch.

FIGURE 6 illustrates a particular liring conduit which could be used inFIGURES 2 and 3 to tire the controlled rectiiiers and which is energizedfrom within the two terminals of the light dimmer structure.

FIGURE 7 illustrates another embodiment of a liring control circuitwhich could be used in FIGURES 2 and 3 where the function of thecontrolled rectiers is replaced by a Triac type device and is energizedfrom the two ter minals of the dimmer structure.

Referring first to FIGURE l which illustrates a prior art arrangement, Ihave illustrated herein an input A-C line which includes wires 10 and 11wherein. a dimmer structure 12, shown as a dotted box, is in series withline 11.

The dimming ballast of FIGURE l is a conventional 3 dimming ballasthaving a primary winding 13 which is connected across the lines I and11, and a series winding 14 which is connected in series with lines 10'and 11 and with the iluorescent tubes, schematically illustrated asltube 15.

The tube 15 is constructed in the usual manner, and is provided withcathodes 16 and 17. Cathode 16 is energized from winding portion 14a ofwinding 14, while cathode 17 is energized from winding portion 13a ofwinding 13.

The dimming circuit control structure 12 may include therein an on-olfswitch 18` and two controlled rectifiers 19 and 20 which are connectedin back-to-back arrangement. T-he gate circuits 21 and 22 of controlledrectiers 19 and 20 are then connected to an appropriate tiring controlcircuit 23'- which will determine the point in each cycle at whichrectiiiers 19 and 20 will lire.

Tube 15 fires because windings 13 and 14 constitute a step-up autotransformer. `Because of the step-up voltage, tube 15 stays ignited evenafter the voltage is cut down by controlled rectifiers 19 and 20.

In such an arrangement, it is possible to have dimming ratios of theorder of -to-1. The circuit, however, is subject to the severedisadvantage that the dimmer control unit 12 has three terminals 24, 25and 26. Thus, if the dimmer is to be installed in a presently existingtwowire system, it -becomes necessary to run an additional wire in thesystem.

Other dimming arrangements have been proposed and used in the pastwherein the dimmer structure does not utilize controlled rectifier-typeelements, but has used an autotransformer, or the like, wherein thevoltage applied directly to lines 10 and 11 and tlhus, the primarywinding 13 of the ballast, is lowered to control the application ofvoltage to tube 15 and, thus, control its intensity.

As previously indicated, these arrangements provide a relatively lowrange of regulation before the tube drops out of illumination.

The principle of the present invention is shown in FIGURE 2, andinvolves the recognition that the controlled rectifier-type scheme, wellknown to the art and shown in FIGURE 1, can be connected in the mannerof the prior art input voltage varying devices for varying tlhe voltageapplied to the ballast primary. However, this novel combination of twoprior art devices results in a device which will give an extremely widerange of dimming, while at the same time, can be directly connected inpresently existing two-wire systems.

Referring to FIGURE 2 where components similar to those of FIGURE 1 havebeen given similar identifying numerals, it will be observed that theonly dilference is that the dimmer structure 12 is connected in front ofthe ballast primary winding 13. This apparently minor modication ofcircuit arrangement, however, leads to a highly desirable dimmerarrangement wlhich can be directly placed in existing two-wire systems,and gives a dimming ratio heretofore impossible to achieve with theregulation type devices available for two-wire systems.

FIGURE 3 illustrates a further modification of the novel arrangement ofFIGURE 2 wherein a radio frequency interference capacitor 30, and adamping resistor 31 are connected in parallel vwith the dimmer circuit12. In addition, FIGURE 3 indicates that further conductor means 32 canbe provided for other ballast primary windings with the single dimmer 12serving to dim` a plurality of individual fluorescent lamps.

In operation, and with the controlled rectiers in series with theballast primary, the sharp turn-on characteristic of controlledrectifiers, or equivalent devices, will cause a voltage peak to appearacross the tube 15 to iire the tube. This inductive voltage peak willoccur at all firing angles of the controlled rectiers 19 and 20, but isespecially important at low ring angles where the peak voltage withoutthe added conductive peak is low.

This can be best understood by reference to FIGURE 4 wherein the waveshape 40 indicates the -voltage applied to primary winding 13, Whilewave shape 41 having the peaks thereon indicates the voltage onsecondary winding 14. At this point of tiring adjustment, it can bepresumed that the light intensity is at the lowest adjustment valuewhich has been found to be consistently of the order of 1% of the fulllight intensity available from the tube 15.

If desired, controlled rectiiiers 19 and 20 may be gate controlledswitches which are inserted in series with the ballast. Gate controlledswitches are devices that can be turned on and off -by a suitable signalapplied to the controlling element of a controlled rectier. A gatecontrolled switch such as the Texas Instruments Type TIX-IZOAO can beturned on and off by a suitable signal applied to the gate whereas aconventional controlled rectifier is turned on with the gate and turnedoff by removing anode current. Such a device can also be bilateral ascompared to the unilateral controlled rectifier.

It is a fundamental property of fluorescent tubes that their lightoutput is directly proportional to the are current flowing through them.If for example the gate controlled switch were made to switch on and olfin a manner indicated by FIGURE 5 the average current would be decreasedand consequently the average light Output would be decreased. Dimming isthereby obtained by varying the average current through the tubes. Againinductive voltage peaks are introduced at the leading edge of theconduction segment, thereby igniting the tube at low voltage levels.Further, iluorescent tubes increase in lumens/ watt in direct proportionto frequency. .Since turning the current on and off a few times duringthe cycle has the eect of increasing frequency, we employ the economicbeneiit of increased lumens/watt, i.e., more light for the sameelectricity.

Note that at this point there must be sufficient operating voltage forthe heaters 16 and 17 of the tu'be, even though this is the point ofminimum RMS voltage available. By way of example, there can be from 1 to2 volts applied to the heaters by windings 13a and 14a at this point ofminimum voltage regulation with the arc current being of the order of0.05 to 2 milliamperes.

It should be further noted that the controlled rectiers or equivalentcontrolled devices, must have a holding current which is less than theminimum current drawn by the ballast and tube.

In order to insure long life for the iluorescent tubes, the heatervoltage should not increase excessively, nor should it be too low andpreferably should be of the order of 21/2 volts at striking. Inaccordance with the invention, however, the voltage applied to theheaters will vary as the dimmer regulates :the applied voltage so thatconstant voltage means of any well known desired type should be providedfor the heaters to prevent application of eX- cessive voltages to theheaters. By way of example, well known saturable reactors can beconnected in parallel with the heaters which will saturate after a givennumber of volt seconds have been applied thereto. Alternatively, and asshown in FIGURE 3 in dotted lines, auxiliary constant voltage sources16a and 17a can be connected to filaments 16 and 17 respectively.

As indicated above, a capacitor 30 is provided for the suppression ofradio frequency interference. A `capacitor of this type can typically beof the order of 0.05 microfarad. However, since this capacitor mayresonate with the inductance ofthe ballast causing an oscillation whichwould interfere with or destroy dimming action, the oscillation ispreferably suppressed by connecting la small resistor 31 in series withcapacitor 30 which could have resistance of the order of ohms. Clearly,other oscillation damping means may be used.

Referring now to FIGURE 6, there is illustrated therein the details ofthe tiring circuit 23 of FIGURES 2 or 3 which is contained in the dimmerstructure 12 and is energized from the two terminals of the dimmerstructure. In FIGURE 6, components identical to those components ofFIGURES 2 and 3, are given identical identifying numerals. Thus, inFIGURE 6 the line 10 having the on-off switch 18 therein, as in FIGURE2, is provided with the radio interference filter comprised of capacitor30 and resistor 31.

FIGURE 6 additionally shows a specific firing circuit for the controlledrectifiers 19 and 20 which includes a series circuit composed ofcapacitors 50 and 51, variable resistor 52 and fixed resistor 53 whichis connected in parallel with controlled rectifiers 19 and 20. Diodes 54and 55 are connected in parallel with capacitors 50 and 51 respectively.Adjustable resistor 52 is provided with fixed parallel resistor 56 andadjustable resistor 57. Common wiper arms 58a, which are driven by anysuitable adjustable knob, varies the resistance of adjustable resistor52, the adjustable resistor 57 serving as a trimmer adjustment foradjustable resistor 52. The junction between capacitor S0 and resistor52 is then connected to one end of trigger 58 which is connected inseries with resistor S9 and the Igate electrode of controlled rectifier20. In .a similar manner, the junction between resistor 52 and capacitor51 is connected through the trigger 60 which is in series with resistor61 and the gate of controlled rectifier 19. The complete assemblage ofFIGURE 6 is then connected in series with reactor 62.

In operation capacitor 50 and adjustable resistor 52 serve as .a phasecontrol circuit for adjusting the firing point of controlled rectifier20 by causing a pulse to be applied to the gate of controlled rectifier20 once the volt- -age at the junction of capacitor 50 and adjustableresistor 52 reaches some predetermined value. The controlled rectifier19 is triggered in an identical manner through the phase control circuitincluding capacitor 51 and trigger 60.

It is to be especially noted that the firing circuit shown in FIGURE 6is connected within the two terminals available within the dimmerstructure since the various components receive line voltage until thetime that their respective rectifiers are fired. After their respectivecomponents have fired, the firing control circuit does not need voltagefor the rest of the half cycle. Once the' half cycle is completed for:their respective control rectifiers, voltage will again appear acrossthe phase components for the new half cycle to prepare it for its nextfiring duty.

Satisfactory results had been obtained with fthe circuit of FIGURE 6using the following component values:

Capacitor 30 0.05 microfarad, 200 volts. Capacitor 50 0.1 microfarad,200 volts. Capacitor 51 0.1 microfarad, 200 volrts. Resistor 31 150ohms.

Resistor 52 700 kilohms.

Resistor 53 2.2 kilohms.

Resistor 56 220 kilohms.

Resistor 57 2 megohms.

Resistor 59 150 ohms.

Resistor 60 150 ohms.

Diode 54 Type 1N485.

Diode 55 Type 1N485.

Trigger diode 58 Type (G E.) ST2X5. Trigger diode 60 Type (G E.) ST2X5.Controlled rectifier 19 Type (GE.) C22B. Controlled rectifier 20 Type(G.E.) C22B.

Reactor 62 25 microhenries, 5 amperes.

FIGURE 7 illustrates a circuit similar to FIGURE 6 in which a triacdevice 70 replaces the function of :the backto-back connected controlledrectifiers 19 and 2.0 of FIG- URE 7. In FIGURE 7, numerals identifyingcomponents similar to those of FIGURES 2, 3 and 6 are given the similaridentifying numerals `whereby the circuit is connected in series withswitch 18 and has the parallel connected resistance-capacitance circuits30-31.

In FIGURE 7, triac 70 is connected in series with the reactor 62 ofFIGURE 6 while a symmetric firing circuit for triac 70 is composed oftrigger diode 71 which is connected through resistor 72 to the phasecontrol circuit composed of capacitor 73, resistors 74 and 75 and p0-tentiometers 76 and 77. The operation of the circuit of FIGURE 7 is suchthat the adjustment of the main adjustment resistor 76 will cause aphase shift in the voltage appearing alt the junction between resistor76 and capacitor 73 so that a firing pulse will be transmitted throughtrigger diode 71 every half cycle dependent upon the amount of phasecontrol which is desired in the firing of triac 70 to obtain the desireddimming operation.

The following values can fbe satisfactorily used for the circuit ofFIGURE 7:

Reactor 62 25 microhenries, 5 amperes.

Although this invention has been described with respect to preferredembodiments thereof, it should be understood that many variations andmodifications will now 'be obvious to those skilled in the art, and itis preferred therefore that the scope of this invention be limited notby the specific disclosure herein ybut only `by the appended f claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are dened as folloiws:

1. In combination for a two-wire power system:

(a) first and second'elongated conductors connected to an A-C source andconstituting the sole electrical power distributing conductors of saidsystem;

(b) a yballast transformer having first and second terminals forconnection to a power source and having secondary heating winding means;

(c) a fiuorescent tube having cathode filament means;

said fluorescent tube connected to said ballast transformer; saidcathode filament means connected to said secondary heating windingmeans;

(d) and a light dimming device having controllable conductive meanstherein for controlling the length of time current can flow therethroughin any half cycle of said A-C source having a first and second leadextending therefrom forming its sole electrical connection to a powersource; said first lead of said light dimming device connected in serieswith one end of said first elongated conductor; said second lead of saidlight dimming device connected to said first terminal of said 'ballasttransformer; said second terminal of said ballast transformer connectedto one end of said second elongated conductor; whereby said lightdimming device is connectable in a two-wire system without requiringinstallation of a third power conducting conductor connected to one ofsaid first and second elongated conductors.

2. The combination of claim 1 wherein said controllable conductive meanscomprises a triac.

3. The combination of claim 1 wherein said lballast transformer containsa first winding portion and a second winding portion; the ends of saidfirst winding portion defining said first and second terminals; saidfirst winding portion, second winding portion and fluorescent tubeconnected in closed series relation.

4. The device substantially as set forth in claim 1 which includes radiofrequency filter means connected 3,344,310 9/ 1967 Nuckolls 315-194OTHER REFERENCES Electrical Design News (EDN): Triac, vol. 9, No.

directly across said controllable conductive means; said radio ltermeans including a series connected capacitor and damping resistor.

5. The combination as set forth in claim 3 wherein said second heatingwinding means comprises Winding portions of said rst and second windingportions, respectively.

lReferences Cited UNITED STATES PATENTS JOHN HUCKERT, Primary Examiner.J. D. CRAIG, Assistant Examiner.

U.S. C1. X.R.

